If I can add something as someone in the UK who perhaps isn't here as their first choice (as much as I appreciate the many wonderful things about the UK, and so many lovely people, there's a reason why a flightless bird is the symbol of the Kiwis, lol), sometimes the only way is through. As in, making your mind up, that this is it for now, and to make the best, and help your daughter make the best of where you are at right now.
We try to focus on the positives (they are there), help our girls focus on the positives, allow them to have a bloody good vent (and us) at home, but remind them that it's impolite to do that with those who this is very much their beloved home, and it will only end in tears,.
The positives range from the amusingly small - M&S gluten free flour is a revelation, as is the free from range, Itsu is to die for, and you can dress in a way that would possibly get the police called, or at the very least, the concerned busybodies association getting in touch with the school, in NZ. To the large - the history is amazing, I'm sorry, I know there are a lot of issues with education over here, but the education our girls have had is far superior to what they would have received in NZ, and they've been challenged and engaged over here while over there they coasted. The teachers, contrary to their mutterings, have been amazing.
Find a friend or family member with similar experiences that you can vent with. And remember, this too shall pass. The world will still be there when your daughter find's her wings, and you can rediscover yours.